It has heretofore been proposed, for example as shown in U.S. Pat. Nos. 2,296,789, 2,595,453, 2,627,424, and 3,810,588, to mount a caster wheel on the tongue of a trailer for swivelling movement about an upright caster axis, to support the trailer tongue when the tongue is not attached to a towing vehicle, and which caster wheel mount was also arranged to allow the caster wheel to be swung from a lower tongue support position, to a raised storage position during towing of the trailer. However, in such prior caster wheel attachments for trailers, the attitude of the caster axis changes from a vertical attitude when the wheel is in its lower position to a horizontal attitude when the wheel is in its raised position. Because of the changing attitude of the caster axis during movement from its lowered to its raised position, such prior caster wheel attachments were not adapted to function as caster wheels at any position other than the fully lowered position. In addition, the change in attitude of the caster axis during movement of the caster wheel from its lowered to its raised position made it difficult to control swivelling of the caster wheel about the caster axis, since the caster wheel tends to gravitate to a position in which the center of mass of the wheel is offset below the caster axis. Further, the caster wheel attachments shown in the aforementioned patents are not positively adjustable between their lowered and raised positions and could not be utilized to adjustably elevate the trailer tongue to facilitate hitching or unhitching of the trailer from the towing vehicle.